1. Field of Invention
This invention relates to inflatable figures formed out of flexible plastic sheet material that is molded to define projections and depressions in the surface of the figure. Typically two plastic sheets of polyvinyl chloride plastic are secured to each other around mated peripheral edges of the sheets, after which air or other gas is pumped into the sealed space within the sheets to form an inflated three dimensional figure.
2. Prior Art Developments
It is known that flat flexible sheets of thin plastic material, e.g. polyvinyl chloride, can be reconfigured into two dimensional shapes by subjecting the sheet to a vacuum forming operation. The vacuum-forming process involves heating a sheet of plastic to its softening temperature, draping the softened sheet over a rigid mold member formed of a porous material, and applying a vacuum force to the underside of the mold member. Air is drawn through the pores (holes) in the mold member, such that the plastic sheet is drawn tightly against the mold member by air suction (vacuum) effect. As the sheet cools from its softened condition it is rigidified into the shape of the mold member surface. The plastic sheet is relatively thin so that it cools relatively quickly while it is lying on the mold member surface. When the air cooled sheet is lifted away from the mold member surface it will retain the two dimensional shape given to it by the vacuum forces derived by air flow through the small holes in the mold member.
U.S. Pat. No. 3,649,152, issued to John Knack on Mar. 14, 1972, discloses a vacuum-forming machine that can be used to form flat plastic sheets into two dimensional shapes.
It is also known that two shaped plastic sheets can be secured together along their mating peripheral edges to form a hollow sealed figure, e.g. a toy clown, toy elephant, or toy football. Pressurized air or other gas can be pumped into the interior space within the hollow figure to define and maintain the desired three dimensional shape of the figure. The final shape of the inflated figure corresponds approximately to the surface contours on the rigid mold members used initially to vacuum-form the component plastic sheets to their two-dimensional shapes (prior to the process of securing the two sheets together).
One problem with the existing methods of manufacturing such inflated figures is that although the plastic sheet material is nominally non-elastic (but flexible), yet when the hollow sheet material figure is pressurized (by pumping air or other gas into the figure) some localized portions of the sheet material figure will expand or deflect outwardly to an undesired extent, thereby distorting the appearance of the figure in its pressurized condition. The present invention is concerned with changes in the manufacturing process intended to minimize or prevent such localized surface distortions.